1. Field of the Invention
This invention relates to the recovery of by-product wastes from the poultry industry as useful products. More particularly the present invention is directed to a method of recovery of aqueous proteinacious calcareous by-products from hatchery operations of the poultry industry. It was discovered that the aqueous by-products containing calcium carbonate could be converted under special conditions to a new protein bonded attrition resistant granular calcium phosphate animal feed mineral and useful carbon dioxide by reaction with phosphoric acid.
2. Description of Related Art
The by-products produced in the operation of hatcheries in the poultry industry include egg shells, proteinacious membranes and residues remaining with the egg shells, feathers, dead chicks and other materials related to the hatching of eggs and recovery of the chicks. These by-products pose a problem of environmentally sound and economical disposal. As the scale of the hatchery operations has increased, the size of the problem and its economic impact on the industry have become matters of serious concern.
In some cases the hatchery by-products are simply landfilled near the hatchery. In more sophisticated operations, trucks collect aqueous hatchery by-products from a number of hatcheries and transport them to a central location where some of the liquid protein is recovered by gravity and the remaining solids are landfilled. In another procedure, the collected hatchery by-products are dried to recover the protein and calcium carbonate values. Although the latter method provides an environmentally sound recovery method, the recovered product has a very low value.
The hatchery by-product is recovered in the hatcheries by wash downs and other methods which introduce water, usually in amounts of 25 to 50 percent. The protein content of the by-product comprises albumen, meat and feather proteins and exhibits an amino acid profile suitable for animal nutrition. The calcium is largely in the form of calcium carbonate in the egg shells which usually comprise the largest source of calcium. Calcium is also derived from calcium carbonate, some calcium phosphate from bones, and small amounts of other calcium salts.
The coreaction of phosphoric acid and calcium carbonate to form calcium phosphates is well known and has been practiced on a very large scale for a long time to produce calcium phosphate as animal feed minerals.
The calcium in hatchery by-product is covered and occluded by proteins, lipoproteins, and other materials so that it has not been possible heretofore to obtain a high degree of reaction of acid with the calcium carbonate. A low degree of reaction leaves large amounts of carbonate unreacted and this dilution keeps the concentrations of phosphorus and calcium low. Any products of the prior art were of low value and not economically competitive with commercially produced calcium phosphates. A low degree of reaction, or a slow reaction, does not produce carbon dioxide in a manner, or amount, where it may be economically recovered for valuable use.
The prior art has not provided a method for preparing attrition resistant granular calcium phosphate and useful carbon dioxide by coreacting calcareous by-products from poultry hatcheries and phosphoric acid.
It is therefore an object of this invention to provide a method of preparing attrition resistant granular proteinacious calcium phosphate animal feed minerals and useful carbon dioxide by coreacting calcareous by-products containing calcium carbonate from poultry hatchery by-products and phosphoric acid.
It is another object to provide the operating parameters of the method which must be followed to successfully carry out the method.
It is a further object of the invention to provide a new and effective protein matrix bonded, attrition resistant, calcium phosphate granular animal feed mineral composition prepared by the new method.
I have now discovered a method of preparing attrition resistant granular proteinacious calcium phosphate animal feed minerals and useful carbon dioxide by coreacting calcareous by-product from poultry hatcheries and phosphoric acid. This method uses a flowable aqueous hatchery by-product containing particles of dry matter amounting to between 35 and 70 percent of the flowable by-product.
The flowable by-product containing protein and calcium moieties in a weight ratio between 0.25 and 1.25 with the calcium moieties consisting essentially of calcium carbonate is comminuted until the particles of dry matter exhibit diameters less than 1 millimeter and the calcium moieties exhibit coreactivity with phosphoric acid.
The comminuted flowable by-product is admixed with an amount of phosphoric acid sufficient to provide between 1.0 and 2.0 molecules of phosphorus per molecule of calcium in the flowable by-product. The phosphoric acid and the reactive calcium moieties are coreacted, at a temperature between 20 and 100xc2x0 C. to form proteinacious calcium phosphate and carbon dioxide gas, until carbon dioxide gas formation ceases and the reacted aqueous flowable by-product exhibits a pH between 2 and 4.
The reacted flowable by-product is admixed with an amount of recycled proteinacious calcium phosphate sufficient to provide a water concentration between 7 and 18 percent in the damp solids formed by the mixing. The damp solids thus formed are rolled by means of a granulator until spheroid granules containing calcium phosphate homogeneously mixed with protein are formed.
The spheroid granules are dried until the protein hardens and forms a matrix bonding the calcium phosphate into attrition resistant granules of animal feed mineral containing between 5 and 20 percent protein, between 12 and 18 percent calcium and between 15 and 24 percent phosphorus.
The instant invention is directed to a method of effectively performing the simple chemical coreaction of calcium carbonate and phosphoric acid to produce calcium phosphate under very difficult conditions. The calcium in hatchery by-product is occluded by proteinacious materials which make its coreaction with phosphoric acid very slow and incomplete. I have now discovered a method whereby the reaction may be expeditiously carried to completion to utilize the protein as a matrix in forming attrition resistant high analysis calcium phosphate animal feed minerals and useful carbon dioxide. The reaction must be performed in flowable aqueous hatchery by-product. To achieve granulation substantial dry recycled animal feed mineral must be mixed with the reacted flowable aqueous hatchery by-product, and the granules formed must be dried until the proteins harden to form a bonding matrix throughout the calcium phosphate granules.
In the instant method of preparing attrition resistant granular proteinacious calcium phosphate animal feed minerals and useful carbon dioxide by coreacting calcareous by-products from poultry hatcheries and phosphoric acid, it was discovered that it was necessary to provide a flowable aqueous hatchery by-product containing particles of dry matter amounting to between 35 and 70 percent of the flowable by-product. When concentrations higher than 70 percent are used, the calcium is not effectively reacted. It is effectively reacted below 35 percent but the amounts of recycle required to form damp solids for granulation are uneconomically large. The dry matter preferably amounts to between 40 and 55 percent of the flowable aqueous hatchery by-product.
It is key to the success of the method that the flowable by-product, containing protein and calcium moieties in a weight ratio between 0.25 and 1.25 with the calcium moieties consisting essentially of calcium carbonate, be comminuted until the particles of dry matter exhibit diameters less than 1 millimeter and that the calcium moieties exhibit coreactivity with phosphoric acid. The amount of protein relative to the calcium controls the hardness and attrition resistance of the granules of animal feed minerals produced. The protein to calcium weight ratio in the flowable aqueous hatchery by-product is preferably between 0.50 and 1.25.
The comminuted flowable by-product must be admixed with an amount of phosphoric acid sufficient to provide between 1.0 and 2.0 molecules of phosphorus per molecule of calcium in the flowable by-product. This is sufficient phosphoric acid to form compounds ranging from monocalcium phosphate to dicalcium phosphate. It is preferable for the complete formation of carbon dioxide gas to provide between 1.5 and 2.0 molecules of phosphorus per molecule of calcium.
It is also preferred that the carbon dioxide formed in the coreaction of the phosphoric acid and the reactive calcium moieties is recovered by reaction with aqueous potassium hydroxide by means of a gas scrubber to form potassium carbonate, which is useful as an animal feed mineral. The gas scrubber may consist of commercial devices including a packed tower, a bubble plate tower, or a spray tower equipped with a demister. The potassium carbonate formed may be dried by conventional means to produce a dry particulate animal feed mineral. It is preferred that the potassium carbonate formed exhibits a potassium to carbonate molecular ratio between 1.5 and 2.0. Higher ratios make it difficult to recover crystalline potassium carbonate, and lower ratios cause inefficient recoveries of the carbon dioxide formed.
The phosphoric acid and the calcium moieties exhibiting coreactivity with phosphoric acid must be coreacted until carbon dioxide gas formation ceases and the reacted aqueous flowable by-product exhibits a pH between 2 and 4. It was found that the phosphoric acid coreacted with the flowable aqueous hatchery by-product could be wet process phosphoric acid so long as the phosphoric acid contained less than 1 part of fluorine per hundred parts of phosphorus by weight.
To make possible effective granulation, the reacted flowable by-product is admixed with an amount of recycled proteinacious calcium phosphate sufficient to provide a water concentration between 7 and 18 percent in the damp solids formed by the mixing. Water concentrations outside the prescribed range do not allow preparation of strong granules.
The damp solids are rolled by means of a granulator until spheroid granules containing calcium phosphate mixed with protein are formed. A conventional cylindrical TVA-type granulator, a rotating double cone, or a pan granulator may be effectively used. The preferred type of granulator employs a pan operating clockwise enclosing a rotor about one-third of the diameter of the pan and operating counterclockwise at between 10 and 100 times the revolutions per minute of the pan.
It is necessary to dry the spheroid granules until the protein hardens and forms a matrix bonding the calcium phosphate into attrition resistant granules of animal feed mineral containing between 5 and 20 percent protein, between 12 and 18 percent calcium and between 15 and 24 percent phosphorus.
The following examples are provided to illustrate the preferred embodiments of the invention.